Pyridazin-3-one derivatives of formula (7):
##STR4##
wherein R.sup.2 and R.sup.3 are independently hydrogen or C.sub.1 -C.sub.3 alkyl, and Q is optionally substituted phenyl, have excellent herbicidal activity, including the following examples: PA1 wherein R.sup.2, R.sup.3 and Q are as defined above, can be easily converted into pyridazin-3-one derivatives of formula (7) and therefore serve as their important intermediates, thereby completing the present invention. PA1 wherein R.sup.2, R.sup.3 and Q are as defined above, which compounds are hereinafter referred to as the present compound(s), a process for their production, and a process for producing pyridazin-3-one derivatives of formula (7): PA1 wherein R.sup.2, R.sup.3 and Q are as defined above, comprising ring closing the compounds of formula (1). PA1 wherein X is hydrogen or halogen; PA1 wherein R.sup.3 and Q are as defined above, with malonic acid derivatives of formula (6): EQU R.sup.2 CH(COOH).sub.2 PA1 (1) The present compounds are added to an aqueous solution of an inorganic base, and the reaction mixture is extracted with an organic solvent, followed by removal of the organic layer. The water layer is concentrated to give the desired salts. In this case, one equivalent of the inorganic base is preferably used for each one equivalent of the present compound. PA1 (2) The present compounds are reacted with an organic base in an organic solvent, and the reaction mixture is concentrated. PA1 wherein R.sup.3 is as defined above and V is iodine, bromine or chlorine, with water in the presence of a base to give carbonyl compounds of formula (9): EQU CF.sub.3 C(.dbd.O)C(.dbd.O)R.sup.3 PA1 wherein Q is as defined above, with nitrous acid, sodium nitrite or other agents under acidic conditions, and then reducing the diazonium salts with stannous chloride or other agents (see, e.g., Organic Synthesis Collective Volume 1, p. 442). PA1 wherein Q is as defined above and R.sup.28 is C.sub.1 -C.sub.6 alkyl. PA1 wherein Q and R.sup.28 are as defined above, in the presence of a base such as sodium acetate or pyridine (see Tetrahedron, vol. 35, p. 2013 (1979)). PA1 1) subsequently effecting the reaction under the conditions described in process 2-2; or PA1 2) adding an acid as exemplified in process 2-4 to the reaction mixture and then effecting the reaction under the conditions described in process 2-4. PA1 wild buckwheat (Polygonum convolvulus), pale smartweed (Polygonum lapathiolium), Pennsylvania smartweed (Polygonum pensylvanicum), ladysthumb (Polygonum persicaria), curly dock (Rumex crispus), broadleaf dock (Rumex obtusifolius), Japanese knotweed (Polygonum cuspidatum) PA1 common purslane (Portulaca oleracea) PA1 common chickweed (Stellaria media) PA1 common lambsquarters (Chenopodium album), kochia (Kochia scoparia) PA1 redroot pigweed (Amaranthus retroflexus), smooth pigweed (Amaranthus hybridus) PA1 wild radish (Raphanus raphanistrium), wild mustard (Sinapis arvensis), shepherdspurse (Capsella bursa-pastoris) PA1 hemp sesbania (Sesbania exaltata), sicklepod (Cassia obtusifolia), Florida beggarweed (Desmodium tortuosum), white clover (Trifolium repens) PA1 velvetleaf (Abutilon theophrasti), prickly sida (Sida spinosa) PA1 field pansy (Viola arvensis), wild pansy (Viola tricolor) PA1 catchweed bedstraw (cleavers) (Galium aparine) PA1 ivyleaf morningglory (Ipomoea hederacea), tall morningglory (Ipomoea purpurea), entireleaf momningglory (Ipomoea hederacea var. integriuscuila), pitted morningglory (Ipomoea lacunosa), field bindweed (Convolvulus arvensis) PA1 red deadnettle (Lamium purpureuim), henbit (Lamiuim amplexicaule) PA1 jimsonweed (Datura stramoniuim), black nightshade (Solanum nigrum) PA1 birdseye speedwell (Veronica persica), ivyleaf speedwell (Veronica hederaefolia) PA1 common cocklebur (Xanthiuim pensylvanicuim), common sunflower (Helianthus annuus), scentless chamomile (Matricaria perforata or inodora), corn marigold (Chrysanthemum segetum), pineappleweed (Matricaria matricarioides), common ragweed (Ambrosia artemisiifolia), giant ragweed (Ambrosia trifida), horseweed (Erigeron canadensis), Japanese mugwort (Artemisia princeps), tall goldenrod (Solidago altissima) PA1 field forget-me-not (Myosotis arvensis) PA1 common milkweed (Asclepias syriaca) PA1 sun spurge (Euphorbia helioscopia), spotted spurge (Euphorbia maculata) PA1 barnyardgrass (Echinochloa crus-galli), green foxtail (Setaria viridis), giant foxtail (Setaria faberi), large crabgrass (Digitaria sanguinalis), goosegrass (Eletisine indica), annual bluegrass (Poa annua), blackgrass (Alopecurus myosuroides), wild oat (Avena fatua), johnsongrass (Sorghum halepense), quackgrass (Agropyron repens), downy brome (Bromus tectorum), bermudagrass (Cynodon dactylon), fall panicum (Panicum dichotomiflorum), Texas panicum (Panicum texantum), shattercane (Sorghum vulgare) PA1 common dayflower (Commelina communis) PA1 field horsetail (Equisetum arvense) PA1 rice flatsedge (Cyperus iria), purple nutsedge (Cyperus rotundus), yellow nutsedge (Cyperus esculentits) PA1 barnyardgrass (Echinochloa oryzicola) PA1 common falsepimpemel (Lindernia procumbens) PA1 Rotala indica, Ammannia multiflora PA1 Elatine triandra PA1 smallflower umbrellaplant (Cyperus difformis), hardstem bulrush (Scirpus juncoides), needle spikerush (Eleocharis acicularis), Cyperus serotinus, Eleocharis kiurogitwai PA1 Monochoria vaginalis PA1 Sagittaria pygmaea, Sagittaria trifolia, Alisma canaticulattim PA1 roundleaf pondweed (Potamogeton distinctus) PA1 Oenanthe javanica
##STR5##
The production of pyridazin-3-one derivatives in a favorable manner is preferred for the development of pyridazine herbicides with excellent activity.